The present invention relates to cooled roofs for electric furnaces.
One of the major trends in present-day electric steel-melting practice is continuous enhancement of both the capacity and specific power of arc steel-making furnaces. Recent years mark the construction of large-capacity electric furnaces which along with converters are considered to be promising in terms of their future development as compared with all other metallurgical units.
Intensification of electric steel-melting production by using gaseous oxygen and higher-rating transformers for melting steels of various chemical composition has, to a considerable extent, deteriorated the operating conditions of the refractory brickwork in electric-arc steel-making furnaces.
The roofs of the electric-arc furnaces are operating under especially severe conditions, being exposed to the combined effect of extremely high temperatures and variable thermal loads, on one hand, and heat products and reducing furnace atmospheres, on the other. All these factors are responsible for reduced strength of the roof brickwork, more irregular wear of roof brick, brickwork deformation and early stoppage of the furnaces, inspite of considerable remaining thickness of their lining, which results in a higher consumption of expensive refractory materials.
Moreover, the present-art roofs of the electric steel-making furnaces are designed so that there is always a danger of the brickwork disruption even before the beginning of operation of the roof, since the brick are wedged to such an extent as to preclude their falling out. Thus, when the furnace roof is erected and then brought into operation, i.e. undergoing heating to a temperature of 1700.degree. to 1800.degree. C., the refractory brick is able neither to elongate nor to expand; its absolute elongation and expansion characteristics in the above temperature range are quite substantial. This gives rise to thermomechanical stresses originating in the roof brickwork, that cause cracking, which, in the case of recurrent heating and cooling cycles, is liable to develop with the ensuring spalling of the refractory lining on the electric furnace roof. Therefore, attempts were made to compensate for the stresses arising in the brickwork in the course of operation of a furnace roof by placing burning-out strips in the roof or using various mortars for laying roof brickwork. It did not, however, produce the desired effect and the life period of furnace roofs extended almost negligibly.
The term of life of the electric furnace roofs was extended by constantly improving the quality of used refractories and developing new kinds of refractory materials and bricks.
However, this trend is inefficient, because the cost of refractories grow constantly and practically out of proportion to the extension of the life period of electric furnace roofs, -- a feature that should not be overlocked.
An alternative that was selected in this search of possiblities and means for extending the life period of the roofs of electric furnaces lay in developing cooled structures.